1. Field of Invention
This invention relates to a process for preparing films. More particularly, the invention relates to the production of polybenzimidazole films.
2. Prior Art
Commonly assigned U.S. Pat. No. 3,836,500, discloses a means for improving the color stability of polybenzimidazole articles. According to the patent, films can be formed by casting from a polybenzimidazole solution. However, no casting conditions are disclosed, nor whether continuous, pinhole-free films are formed.
In commonly assigned U.S. Pat. No. 4,048,139, polybenzimidazole films are formed by casting a polybenzimidazole solution and then evaporating the polybenzimidazole solvent. However, a continuous process for preparing continuous, pinhole-free polybenzimidazole films is not disclosed.
Prior to the instant invention, there was no commercially feasible process for preparing polybenzimidazole films. In the prior art, solvent evaporation was conducted at such high temperatures that, after part of the solvent was removed, a skin of what appeared to be a polymer-solvent complex formed which made the subsequent removal of the remaining solvent much more difficult. Drying times tended to be very long and the films usually had to be washed for up to 24 hours to remove residual solvent from the film. Consequently, it was commercially infeasible to manufacture polybenzimidazole films using the known prior art processes. In addition, there was no known continuous process for preparing continuous, pinhole-free polybenzimidazole films.
Accordingly, it is an object of this invention to prepare continuous polybenzimidazole films.
It is another object of this invention to prepare continuous polybenzimidazole films in a continuous process.
It is also an object of this invention to prepare polybenzimidazole films which are pinhole-free.
It is a further object of this invention to prepare polybenzimidazole films that are useful in high temperature applications.
These and other objects are obtained by employing the process of the instant invention.